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s390/vfio-ap: replace open coded locks for VFIO_GROUP_NOTIFY_SET_KVM …
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…notification

It was pointed out during an unrelated patch review that locks should not
be open coded - i.e., writing the algorithm of a standard lock in a
function instead of using a lock from the standard library. The setting and
testing of a busy flag and sleeping on a wait_event is the same thing
a lock does. The open coded locks are invisible to lockdep, so potential
locking problems are not detected.

This patch removes the open coded locks used during
VFIO_GROUP_NOTIFY_SET_KVM notification. The busy flag
and wait queue were introduced to resolve a possible circular locking
dependency reported by lockdep when starting a secure execution guest
configured with AP adapters and domains. Reversing the order in which
the kvm->lock mutex and matrix_dev->lock mutex are locked resolves the
issue reported by lockdep, thus enabling the removal of the open coded
locks.

Signed-off-by: Tony Krowiak <akrowiak@linux.ibm.com>
Acked-by: Halil Pasic <pasic@linux.ibm.com>
Link: https://lore.kernel.org/r/20210823212047.1476436-3-akrowiak@linux.ibm.com
Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
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Tony Krowiak authored and Alex Williamson committed Aug 24, 2021
1 parent 1e75373 commit 86956e7
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Showing 3 changed files with 67 additions and 98 deletions.
31 changes: 27 additions & 4 deletions arch/s390/kvm/kvm-s390.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -2559,12 +2559,26 @@ static void kvm_s390_set_crycb_format(struct kvm *kvm)
kvm->arch.crypto.crycbd |= CRYCB_FORMAT1;
}

/*
* kvm_arch_crypto_set_masks
*
* @kvm: pointer to the target guest's KVM struct containing the crypto masks
* to be set.
* @apm: the mask identifying the accessible AP adapters
* @aqm: the mask identifying the accessible AP domains
* @adm: the mask identifying the accessible AP control domains
*
* Set the masks that identify the adapters, domains and control domains to
* which the KVM guest is granted access.
*
* Note: The kvm->lock mutex must be locked by the caller before invoking this
* function.
*/
void kvm_arch_crypto_set_masks(struct kvm *kvm, unsigned long *apm,
unsigned long *aqm, unsigned long *adm)
{
struct kvm_s390_crypto_cb *crycb = kvm->arch.crypto.crycb;

mutex_lock(&kvm->lock);
kvm_s390_vcpu_block_all(kvm);

switch (kvm->arch.crypto.crycbd & CRYCB_FORMAT_MASK) {
Expand Down Expand Up @@ -2595,13 +2609,23 @@ void kvm_arch_crypto_set_masks(struct kvm *kvm, unsigned long *apm,
/* recreate the shadow crycb for each vcpu */
kvm_s390_sync_request_broadcast(kvm, KVM_REQ_VSIE_RESTART);
kvm_s390_vcpu_unblock_all(kvm);
mutex_unlock(&kvm->lock);
}
EXPORT_SYMBOL_GPL(kvm_arch_crypto_set_masks);

/*
* kvm_arch_crypto_clear_masks
*
* @kvm: pointer to the target guest's KVM struct containing the crypto masks
* to be cleared.
*
* Clear the masks that identify the adapters, domains and control domains to
* which the KVM guest is granted access.
*
* Note: The kvm->lock mutex must be locked by the caller before invoking this
* function.
*/
void kvm_arch_crypto_clear_masks(struct kvm *kvm)
{
mutex_lock(&kvm->lock);
kvm_s390_vcpu_block_all(kvm);

memset(&kvm->arch.crypto.crycb->apcb0, 0,
Expand All @@ -2613,7 +2637,6 @@ void kvm_arch_crypto_clear_masks(struct kvm *kvm)
/* recreate the shadow crycb for each vcpu */
kvm_s390_sync_request_broadcast(kvm, KVM_REQ_VSIE_RESTART);
kvm_s390_vcpu_unblock_all(kvm);
mutex_unlock(&kvm->lock);
}
EXPORT_SYMBOL_GPL(kvm_arch_crypto_clear_masks);

Expand Down
132 changes: 40 additions & 92 deletions drivers/s390/crypto/vfio_ap_ops.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -294,15 +294,6 @@ static int handle_pqap(struct kvm_vcpu *vcpu)
matrix_mdev = container_of(vcpu->kvm->arch.crypto.pqap_hook,
struct ap_matrix_mdev, pqap_hook);

/*
* If the KVM pointer is in the process of being set, wait until the
* process has completed.
*/
wait_event_cmd(matrix_mdev->wait_for_kvm,
!matrix_mdev->kvm_busy,
mutex_unlock(&matrix_dev->lock),
mutex_lock(&matrix_dev->lock));

/* If the there is no guest using the mdev, there is nothing to do */
if (!matrix_mdev->kvm)
goto out_unlock;
Expand Down Expand Up @@ -350,7 +341,6 @@ static int vfio_ap_mdev_create(struct mdev_device *mdev)

matrix_mdev->mdev = mdev;
vfio_ap_matrix_init(&matrix_dev->info, &matrix_mdev->matrix);
init_waitqueue_head(&matrix_mdev->wait_for_kvm);
mdev_set_drvdata(mdev, matrix_mdev);
matrix_mdev->pqap_hook = handle_pqap;
mutex_lock(&matrix_dev->lock);
Expand Down Expand Up @@ -619,11 +609,8 @@ static ssize_t assign_adapter_store(struct device *dev,

mutex_lock(&matrix_dev->lock);

/*
* If the KVM pointer is in flux or the guest is running, disallow
* un-assignment of adapter
*/
if (matrix_mdev->kvm_busy || matrix_mdev->kvm) {
/* If the KVM guest is running, disallow assignment of adapter */
if (matrix_mdev->kvm) {
ret = -EBUSY;
goto done;
}
Expand Down Expand Up @@ -692,11 +679,8 @@ static ssize_t unassign_adapter_store(struct device *dev,

mutex_lock(&matrix_dev->lock);

/*
* If the KVM pointer is in flux or the guest is running, disallow
* un-assignment of adapter
*/
if (matrix_mdev->kvm_busy || matrix_mdev->kvm) {
/* If the KVM guest is running, disallow unassignment of adapter */
if (matrix_mdev->kvm) {
ret = -EBUSY;
goto done;
}
Expand Down Expand Up @@ -782,11 +766,8 @@ static ssize_t assign_domain_store(struct device *dev,

mutex_lock(&matrix_dev->lock);

/*
* If the KVM pointer is in flux or the guest is running, disallow
* assignment of domain
*/
if (matrix_mdev->kvm_busy || matrix_mdev->kvm) {
/* If the KVM guest is running, disallow assignment of domain */
if (matrix_mdev->kvm) {
ret = -EBUSY;
goto done;
}
Expand Down Expand Up @@ -850,11 +831,8 @@ static ssize_t unassign_domain_store(struct device *dev,

mutex_lock(&matrix_dev->lock);

/*
* If the KVM pointer is in flux or the guest is running, disallow
* un-assignment of domain
*/
if (matrix_mdev->kvm_busy || matrix_mdev->kvm) {
/* If the KVM guest is running, disallow unassignment of domain */
if (matrix_mdev->kvm) {
ret = -EBUSY;
goto done;
}
Expand Down Expand Up @@ -904,11 +882,8 @@ static ssize_t assign_control_domain_store(struct device *dev,

mutex_lock(&matrix_dev->lock);

/*
* If the KVM pointer is in flux or the guest is running, disallow
* assignment of control domain.
*/
if (matrix_mdev->kvm_busy || matrix_mdev->kvm) {
/* If the KVM guest is running, disallow assignment of control domain */
if (matrix_mdev->kvm) {
ret = -EBUSY;
goto done;
}
Expand Down Expand Up @@ -963,11 +938,8 @@ static ssize_t unassign_control_domain_store(struct device *dev,

mutex_lock(&matrix_dev->lock);

/*
* If the KVM pointer is in flux or the guest is running, disallow
* un-assignment of control domain.
*/
if (matrix_mdev->kvm_busy || matrix_mdev->kvm) {
/* If a KVM guest is running, disallow unassignment of control domain */
if (matrix_mdev->kvm) {
ret = -EBUSY;
goto done;
}
Expand Down Expand Up @@ -1108,28 +1080,30 @@ static int vfio_ap_mdev_set_kvm(struct ap_matrix_mdev *matrix_mdev,
struct ap_matrix_mdev *m;

if (kvm->arch.crypto.crycbd) {
down_write(&kvm->arch.crypto.pqap_hook_rwsem);
kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook;
up_write(&kvm->arch.crypto.pqap_hook_rwsem);

mutex_lock(&kvm->lock);
mutex_lock(&matrix_dev->lock);

list_for_each_entry(m, &matrix_dev->mdev_list, node) {
if (m != matrix_mdev && m->kvm == kvm)
if (m != matrix_mdev && m->kvm == kvm) {
mutex_unlock(&kvm->lock);
mutex_unlock(&matrix_dev->lock);
return -EPERM;
}
}

kvm_get_kvm(kvm);
matrix_mdev->kvm = kvm;
matrix_mdev->kvm_busy = true;
mutex_unlock(&matrix_dev->lock);

down_write(&matrix_mdev->kvm->arch.crypto.pqap_hook_rwsem);
kvm->arch.crypto.pqap_hook = &matrix_mdev->pqap_hook;
up_write(&matrix_mdev->kvm->arch.crypto.pqap_hook_rwsem);

kvm_arch_crypto_set_masks(kvm,
matrix_mdev->matrix.apm,
matrix_mdev->matrix.aqm,
matrix_mdev->matrix.adm);

mutex_lock(&matrix_dev->lock);
matrix_mdev->kvm_busy = false;
wake_up_all(&matrix_mdev->wait_for_kvm);
mutex_unlock(&kvm->lock);
mutex_unlock(&matrix_dev->lock);
}

return 0;
Expand Down Expand Up @@ -1179,35 +1153,24 @@ static int vfio_ap_mdev_iommu_notifier(struct notifier_block *nb,
* done under the @matrix_mdev->lock.
*
*/
static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev)
static void vfio_ap_mdev_unset_kvm(struct ap_matrix_mdev *matrix_mdev,
struct kvm *kvm)
{
/*
* If the KVM pointer is in the process of being set, wait until the
* process has completed.
*/
wait_event_cmd(matrix_mdev->wait_for_kvm,
!matrix_mdev->kvm_busy,
mutex_unlock(&matrix_dev->lock),
mutex_lock(&matrix_dev->lock));

if (matrix_mdev->kvm) {
matrix_mdev->kvm_busy = true;
mutex_unlock(&matrix_dev->lock);

if (matrix_mdev->kvm->arch.crypto.crycbd) {
down_write(&matrix_mdev->kvm->arch.crypto.pqap_hook_rwsem);
matrix_mdev->kvm->arch.crypto.pqap_hook = NULL;
up_write(&matrix_mdev->kvm->arch.crypto.pqap_hook_rwsem);

kvm_arch_crypto_clear_masks(matrix_mdev->kvm);
}
if (kvm && kvm->arch.crypto.crycbd) {
down_write(&kvm->arch.crypto.pqap_hook_rwsem);
kvm->arch.crypto.pqap_hook = NULL;
up_write(&kvm->arch.crypto.pqap_hook_rwsem);

mutex_lock(&kvm->lock);
mutex_lock(&matrix_dev->lock);

kvm_arch_crypto_clear_masks(kvm);
vfio_ap_mdev_reset_queues(matrix_mdev->mdev);
kvm_put_kvm(matrix_mdev->kvm);
kvm_put_kvm(kvm);
matrix_mdev->kvm = NULL;
matrix_mdev->kvm_busy = false;
wake_up_all(&matrix_mdev->wait_for_kvm);

mutex_unlock(&kvm->lock);
mutex_unlock(&matrix_dev->lock);
}
}

Expand All @@ -1220,16 +1183,13 @@ static int vfio_ap_mdev_group_notifier(struct notifier_block *nb,
if (action != VFIO_GROUP_NOTIFY_SET_KVM)
return NOTIFY_OK;

mutex_lock(&matrix_dev->lock);
matrix_mdev = container_of(nb, struct ap_matrix_mdev, group_notifier);

if (!data)
vfio_ap_mdev_unset_kvm(matrix_mdev);
vfio_ap_mdev_unset_kvm(matrix_mdev, matrix_mdev->kvm);
else if (vfio_ap_mdev_set_kvm(matrix_mdev, data))
notify_rc = NOTIFY_DONE;

mutex_unlock(&matrix_dev->lock);

return notify_rc;
}

Expand Down Expand Up @@ -1363,14 +1323,11 @@ static void vfio_ap_mdev_close_device(struct mdev_device *mdev)
{
struct ap_matrix_mdev *matrix_mdev = mdev_get_drvdata(mdev);

mutex_lock(&matrix_dev->lock);
vfio_ap_mdev_unset_kvm(matrix_mdev);
mutex_unlock(&matrix_dev->lock);

vfio_unregister_notifier(mdev_dev(mdev), VFIO_IOMMU_NOTIFY,
&matrix_mdev->iommu_notifier);
vfio_unregister_notifier(mdev_dev(mdev), VFIO_GROUP_NOTIFY,
&matrix_mdev->group_notifier);
vfio_ap_mdev_unset_kvm(matrix_mdev, matrix_mdev->kvm);
module_put(THIS_MODULE);
}

Expand Down Expand Up @@ -1412,15 +1369,6 @@ static ssize_t vfio_ap_mdev_ioctl(struct mdev_device *mdev,
break;
}

/*
* If the KVM pointer is in the process of being set, wait until
* the process has completed.
*/
wait_event_cmd(matrix_mdev->wait_for_kvm,
!matrix_mdev->kvm_busy,
mutex_unlock(&matrix_dev->lock),
mutex_lock(&matrix_dev->lock));

ret = vfio_ap_mdev_reset_queues(mdev);
break;
default:
Expand Down
2 changes: 0 additions & 2 deletions drivers/s390/crypto/vfio_ap_private.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -83,8 +83,6 @@ struct ap_matrix_mdev {
struct ap_matrix matrix;
struct notifier_block group_notifier;
struct notifier_block iommu_notifier;
bool kvm_busy;
wait_queue_head_t wait_for_kvm;
struct kvm *kvm;
crypto_hook pqap_hook;
struct mdev_device *mdev;
Expand Down

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